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Abstract

During 2014 and 2015 three experiments, were conducted, the first two at the Agricultural Experimental Station (AES) in Isabela and the third at the Small Animal Farm of the Animal Science Department in Lajas. The objective of Expt. 1 was to evaluate two forage soybeans (cv. Hinson and line 22-3) in phenological growth stages (PGS; R3 and R6); and sunflowers (var. Camaro and Torino) at R6 and R8, to assess effects on dry matter yield (DMY), nutritional value, fermentation characteristics and aerobic stability of silage. A randomized complete block design (RCBD) was used with four replications in a split plot arrangement; in which the blocking criterion was the planting record, the main plot represented the variety, and the sub-plot the growth stage. The forages were ensiled in micro-silos of 15 L (Expt. 2 and soybean in Expt. 1) and 50 L (sunflower in Expt. 1 and 3) capacity. An analysis of variance showed that for soybean, the dry-matter (DM) content differed significantly (p < 0.05) between PGS, R3 and R6 (19.50 vs 24.85%), but not between cv. Hinson y line 22-3. There was an interaction of variety x PGS (p < 0.05), line 22-3 having the highest DMY (7.2 Mg ha-1 ) at the R6 but not at the R3 stage. Only 22-3 line was selected for further evaluation. Significant differences were found (p < 0.05) between the R3 and R6 PGS for DM (18 vs 24%), neutral detergent fiber (NDF; 51 vs 56%) and net energy for lactation (NEL; 1.25 vs 1.19 Mcal kg-1 DM), whereas crude protein (CP; 18%), acid detergent fiber (ADF; 46%), total digestible nutrients (TDN; 57%) and relative feed value (RFV; 94) were not different (p > 0.05) between PGS. As for fermentation characteristics, difference was found (p < 0.05) between PGS in pH, acetic acid content, lactic / acetic ratio and propionic acid, but there were no differences (p > 0.05) in lactic acid (2.14%), butyric acid (3.64%) and ammonia nitrogen as a percentage of total nitrogen (NH3-N; 33%). Silage at R6 gave the lowest pH (4.98), acetic (2.95%) and propionic acid (0.18%) contents, and the highest lactic/acetic ratio (0.97). Aerobic stability evaluated during 7 days of exposition to air showed no difference (p > 0.05) between PGS in pH and temperature, but time remaining stable was longer (p < 0.05) in R3 (156 h). As for the sunflower crop, the analysis shows difference (p < 0.05) in forage DM between PGS R6 and R8 (15.4 vs 23%), but not between varieties. However, there was no difference (p > 0.05) in DMY (7.1 Mg ha-1 ) neither between varieties nor PGS. Silage fermentation characteristics of sunflower were determined in var. Torino only and differences (p < 0.05) were found between R6 and R8 in DM (14 vs 22%), NDF (43 vs 50%), TDN (68.5 vs 66.2%), NEL (1.60 vs 1.55 Mcal kg-1 DM) and RFV (136 vs 109), but not (p > 0.05) in CP (11%) and ADF (36%). Regarding fermentation characteristics, PGS R6 and R8, differed (p < 0.05) in pH (3.8 vs. 4.3), lactic acid (12.5 vs 8%) and acetic acid (2.4 vs 1.8%), but not (p > 0.05) in butyric acid (0.7%), propionic acid (0.09%) and ammonia nitrogen as a percentage of total nitrogen (5.75%). Aerobic stability evaluation of the Torino variety showed no effect (p > 0.05) of PGS (pH, temperature and stability time). For both soybean and sunflower the length of aerobic exposure time had an effect (p < 0.05) on silage pH and temperature. In soybean data, pH and temperature values were not different until the fifth and third days, respectively; whereas in sunflower silage these differences were apparent after the first day. These results indicate a poor fermentation of the soybean silage. The PGS R6 showed the best conditions for the preparation of soybean and sunflower silages. In order to improve the fermentation, the possible use of additives is suggested. Expt. 2 involved evaluation of three silages each of soybean (S) and sunflower (SUN) ensiled at PGS R6 [single forage; forage with 6% molasses (M), and in mixture with sorghum (SOR)]. The forages were fermented in 15-L micro-silos and sampled after 30 days of fermentation. Fermentation and nutritional value data were subjected to analysis of variance in a completely randomized design with four replications. The soybean-sorghum mixture (SSOR) had the highest DMY (4.0 Mg ha-1 ) (p < 0.05) and mean values of 32% DM, 16% CP, 54% TDN, 1.13 Mcal ENL kg-1 DM and 103 RFV. These values were lower (p < 0.05) than those obtained for soybean alone (S) and soybean with molasses (SM). The highest NDF content (p < 0.05) was observed in SSOR (56%), but there was no difference (p > 0.05) between treatments in ADF (35%). Addition of molasses and admixture with sorghum improved (p < 0.05) the fermentation characteristics of soybean silage in pH, organic acids, ammonium equivalent protein (AEP) and NH3-N. From a nutritional standpoint, the addition of molasses appears to be the best option for soybean silage preparation, because it did not adversely affect CP, ADF, NDF nor energy level (TDN and NE). However, if maximum forage yield is desired the soybean-sorghum mixture may be advantageous. The SSOR gave mean values of 4.13 pH, 7.82% lactic acid, 2.88% acetic acid, 0.03% butyric acid and 8.25% NH3-N. The pH, lactic acid and NH3-N values of SSOR were different (p < 0.05) from both S and SM, but acetic acid and butyric acid content differed only relative to S. As for aerobic stability, there were differences (p < 0.05) between treatments in pH, with values of 4.75, 4.35 and 4.04 for S, SM and SSOR, respectively. However, the SSOR silage had the highest (p < 0.05) temperature and loss of DM, as well as a shorter stability time (although not significant). Regression analysis showed a quadratic relationship (p < 0.05) between time of exposure to air and temperature of the silage. In this experiment the DMY was also higher (p < 0.05) for SUN in mixture with sorghum (SUNSOR; 5.4 Mg ha-1 ). Sunflower silages with molasses (SUNM) and SUNSOR had higher (p < 0.05) DM content (18%) than SUN alone (16%); in addition, the SUNSOR silage showed the highest CP level (13%). No differences (p > 0.05) in ADF (36%) were found between SUNSOR and SUN, but both exceeded (p < 0.05) SUNM (29%). The three treatments were different (p < 0.05) in NDF and NEL, SUNSOR having the highest NDF content (50%) and the lowest energy level (1.21 Mcal kg-1 DM); while SUNM had the lowest level of NDF (39%) and the highest of NEL (1.36 Mcal kg-1 DM). Regarding fermentation characteristics, SUNM and SUNSOR showed the best values of pH (3.9), propionic acid (0.01%), butyric acid (0.04%) and NH3-N (5.21%), differing (p < 0.05) from SUN. Lactic (11%) and acetic acids (3%) did not differ (p > 0.05) between silages. The aerobic stability, evaluated by temperature and pH changes, did not show effects (p > 0.05) of treatments. However SUNM showed a shorter stability time and greater loss of DM (p < 0.05) than SUN. The air exposure time affected (p < 0.05) aerobic stability of SUN silage, as shown by increasing pH and temperature. Adding 6% molasses to SUN silage produced a dilution effect on the NDF and ADF fractions, and an increase in energy level (TDN and NE), thus resulting in a better RFV. Both soybean and SUN mixtures with sorghum increased DMY and FDN levels, and decreased the NE value. The inclusion of molasses and mixture with SOR improved fermentation characteristics of both soybean and SUN silages (improving levels of pH, propionic acid, butyric acid and NH3-N). However, the addition of molasses also generated a greater loss of DM and a lower stability of SUN silage. Expt. 3 focused on the animal acceptability of SUN, SUNM y SUNSOR silages. Silage intake was recorded in a cafeteria trial using sheep (21 kg mean live weight) during 2 hours of access daily over a period of 12 days to calculate the coefficient of preference (CoP). An analysis of variance using a RCBD with 7 repetitions revealed CoP differences (p < 0.05) between treatments, being highest for SUNSOR (1.53) based on a consumption of 0.93 kg DM day-1 . Sunflower-molasses silage had a strong ethanol odor and poor acceptability, with a CoP of 0.44. Thus addition of molasses decreased intake of SUN silage, while the mixture with sorghum improved its acceptability. The SUNSOR and SUN silages deserve further research including assessment of their effect on productive performance of ruminants.